Re: Re: ATT: Rick Denney


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Posted by fred boyd on October 16, 2003 at 14:11:39:

In Reply to: Re: ATT: Rick Denney posted by Mark Wiseman on October 16, 2003 at 13:02:08:

Ok Mark, here's another two cents (for a total of 4) about WHY pitch seems to go up as air temperature goes up. Again, let's hear from one of those PHD-types for a definitive answer.

The expansion and contraction with temperature of metal tubing has almost nothing to do with subsequent pitch. Indeed, if colder metal contracts, and is therefore shorter, then the resulting pitch should go up. But nooooooo, it goes down and we must push in slides to keep the eletronic tuner green.

The reason pitch seems to vary with temperature, is that the speed of sound through air increases as temperature rises, and slows as air is cooled. This applies only to the air inside of our instruments, not the ambient air. Once the vibrations leave the bell, they travel to the listener's ears intact. That is to say, that the apparent pitch is not affected by the temperature of the ambient air. It is the functioning air (inside the horn) that produces the initial pitch. As we warm up the horn, the inside air warms up and affects the pitch.

OK, so sound travels faster in warmer air, and slower in cooler air. We depend on a particular length of tubing to provide the resonance for any particular pitch. ( Oh yeah, vibrations don't necessarily determine pitch. Our ears/brains are imperfect, and other factors the perceived pitch). If one particular length of tubing is perfect at any given temperature to produce a pitch, faster traveling sound (at a higher temperature) will, now, finish it's cycle in a greater distance...slightly longer wave length for the same pitch. By the time the air has vibrated X-number of times, it will have traveled a greater distance in warmer (faster) air. Hence, a longer tube is required to compensate for the warmer/faster air...pull out the tuning slide.

Likewise, colder/slower air will not travel quite as far by the time X-number of vibrations happen. A slightly shorter wave length for the same frequency. Push in the tuning slide to compensate.

Yes, the physical length of brass is longer when warm, but it is a minute factor compared to the increase in the speed of sound and longer resulting wave length.

So, why worry about all this crap? Just do what you always do...listen, push, pull, lip, re-finger, or whatever it takes to play in tune and don't worry about "why".

So, to answer your question about the inside diameter of heated tubing, my guess is that it also is larger. Si?

Ouch! My tiny brain is over heating due to the increased speed, yada, yada, yada.

fred



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